Method for engine braking a vehicle having a continuously variable transmission

ABSTRACT

A method for controlling an internal combustion engine of a vehicle having a continuously variable transmission is disclosed. When a driven pulley speed is less than a predetermined driven pulley speed and an actual engine speed is less than an engine speed causing a driving pulley speed to be a driving pulley engagement speed: controlling the engine to increase the actual engine speed to increase the driving pulley speed to be at least the driving pulley engagement speed. When the driven pulley speed is above the predetermined driven pulley speed, the actual engine speed is greater than the engine speed causing the driving pulley speed to be the driving pulley engagement speed, and the desired engine speed is less than the engine speed causing the driving pulley speed to be the driving pulley engagement speed: controlling the engine to operate under conditions corresponding to an engine braking speed.

CROSS-REFERENCE

The present application is a divisional application of U.S. patentapplication Ser. No. 16/277,404, filed Feb. 15, 2019, which is adivisional application of U.S. patent application Ser. No. 15/531,918,filed May 31, 2017, which is a National Phase Entry Application ofInternational Patent Application No. PCT/IB2016/052458, filed Apr. 29,2016, which claims priority to U.S. Provisional Patent Application No.62/155,039, filed Apr. 30, 2015, the entirety of all of which isincorporated herein by reference.

TECHNICAL FIELD

The present technology relates to a method for engine braking a vehiclehaving a continuously variable transmission.

BACKGROUND

In a wheeled vehicle powered by an internal combustion engine, when thedriver releases the throttle operator, such as the throttle pedal, thethrottle valve almost completely closes. As a result very little air canbe supplied to the engine. When this happens, if the vehicle is inmovement and the engine is still connected to the wheels, the wheelswant to turn the crankshaft of the engine at a speed corresponding tothe speed required to move the vehicle at the speed the vehicle iscurrently going. However, because of the position of the throttle valve,a vacuum is created in the engine, and the torque applied on thecrankshaft by the wheels needs to work against this vacuum. As a result,the engine slows down the vehicle or, in the case of a vehicle goingdown a hill, at least reduces the vehicle's acceleration. This is knownas engine braking.

One of the main advantages of engine braking is that, by assisting inreducing the speed of the vehicle, it can help reduce wear on the brakesnormally used to brake the wheels.

Certain vehicles are provided with a continuously variable transmission(CVT) to transfer torque from the engine to the wheels. A CVT has adriving pulley, a driven pulley and a belt looped around the pulleys totransmit torque between the pulleys. In most situations for a vehiclehaving a CVT, releasing the throttle operator would result in enginebraking.

However, some CVTs have a driving pulley that is actuated centrifugally.Centrifugally actuated driving pulleys have a pair of sheaves that movecloser together as the speed of the driving pulley increases. As such,in some centrifugally actuated driving pulleys, at low driving pulleyspeeds the sheaves are too far apart to clamp the belt therebetween.Therefore, releasing the throttle pedal when the driving pulley speed islow would not result in engine braking since the belt turns freelyrelative to the driving pulley and the rotation of the wheels and thedriven pulley is not opposed by the engine's resistance. This wouldoccur for example when a vehicle starts going down a hill from rest withthe engine idling.

In order to address this problem, some centrifugally actuated drivingpulleys are provided with a clutch, or other mechanism to cause the beltto transfer torque to the crankshaft of the engine if the belt turnsfreely relative to the driving pulley. In one example, the drivingpulley is provided with an overrunning clutch which causes the belt toapply torque to the crankshaft if it turns relative to thecrankshaft/driving pulley by more than a certain speed. When theoverrunning clutch is engaged, engine braking is applied.

Although these mechanisms provide a solution to the problem of theengine not providing engine braking under certain conditions, they alsoadd cost, weight and complexity to the vehicle.

It would therefore be desirable to provide a solution to the problem ofvehicles having a CVT with a centrifugally actuated driving pulley thatdo not have engine braking under certain conditions.

SUMMARY

It is an object of the present to ameliorate at least some of theinconveniences present in the prior art.

According to an aspect of the present technology, there is provided amethod for controlling an internal combustion engine of a vehicle. Thevehicle has the internal combustion engine and a continuously variabletransmission (CVT). The CVT has a driving pulley operatively connectedto the engine, a driven pulley, and a belt looped around the driving anddriven pulleys, the belt transmitting torque between the driving anddriven pulleys. The vehicle also has at least one ground engaging memberoperatively connected to the driven pulley. The method comprises:determining a first speed, the first speed being proportional to adriven pulley speed; determining an idle speed set point based at leastin part on the first speed, the idle speed set point being less than anengagement speed when the driven pulley speed is less than apredetermined driven pulley speed, the idle speed set point being lessthan an actual engine speed when the driven pulley speed is greater thanthe predetermined driven pulley speed; determining a desired enginespeed; and controlling the engine to operate under conditionscorresponding to the idle speed set point when the desired engine speedis less than the idle speed set point, controlling the engine to operateunder conditions corresponding to the idle speed set point causingengine braking when the driven pulley speed is greater than thepredetermined driven pulley speed.

According to some implementations of the present technology, the idlespeed set point is greater than the engagement speed when the drivenpulley speed is greater than the predetermined driven pulley speed.

According to some implementations of the present technology, when thedriven pulley speed is less than the predetermined driven pulley speed,the idle speed set point increases as the driving pulley speedincreases.

According to some implementations of the present technology, determiningthe idle speed set point comprises multiplying the driven pulley speedby a CVT target ratio.

According to some implementations of the present technology, determiningthe idle speed set point further comprises subtracting an engine speedoffset from a result of the driven pulley speed being multiplied by theCVT target ratio.

According to some implementations of the present technology, the CVTtarget ratio is based on the actual engine speed.

According to some implementations of the present technology, the enginespeed offset increases as the actual engine speed increases.

According to some implementations of the present technology, the vehiclealso has a geared transmission operatively connecting the at least oneground engaging member to the driven pulley. The first speed is a speedof a rotating element operatively connecting the geared transmission tothe at least one ground engaging member. The method further comprisesdetermining a drive mode of the geared transmission. The driven pulleyspeed is determined by multiplying the first speed by a gear ratiocorresponding to the drive mode.

According to some implementations of the present technology, the methodfurther comprises determining a throttle operator position. The desiredengine speed is based at least in part on the throttle operatorposition.

According to some implementations of the present technology, controllingthe engine to operate under conditions corresponding to the idle speedset point when the driven pulley speed is greater than the predeterminedrange of driven pulley speeds comprises: positioning a valve controllinga supply of air to the engine at a position that is less than a positionthat would be necessary to operate the engine at the actual enginespeed.

According to some implementations of the present technology, the valveis a throttle valve of a throttle body.

According to some implementations of the present technology, the methodfurther comprises determining an actual engine speed.

According to some implementations of the present technology, determiningthe actual engine speed includes determining a speed of rotation of adriveshaft operatively connecting the engine to the at least one groundengaging member.

According to some implementations of the present technology, determiningthe actual engine speed includes determining a vehicle speed.

According to some implementations of the present technology, theengagement speed is a driving pulley engagement speed.

According to some implementations of the present technology, the vehiclealso has a centrifugal clutch operatively connecting the driving pulleyto the engine. The engagement speed is a clutch engagement speed.

According to another aspect of the present technology, there is provideda method for controlling an internal combustion engine of a vehiclegoing downhill with a throttle operator in an idle position. The vehiclehas the internal combustion engine, the throttle operator, and acontinuously variable transmission (CVT). The CVT has a driving pulleyoperatively connected to the engine, a driven pulley, and a belt loopedaround the driving and driven pulleys, the belt transmitting torquebetween the driving and driven pulleys. The vehicle also has at leastone ground engaging member operatively connected to the driven pulley.The driven pulley initially has a driven pulley speed below apredetermined driven pulley speed. The method comprises: determining afirst speed, the first speed being proportional to the driven pulleyspeed; as the driven pulley speed increases and the driven pulley speedis below the predetermined driven pulley speed, increasing an actualengine speed as the driven pulley speed increases; the actual enginespeed being an engagement speed when the driven pulley speed is thepredetermined driven pulley speed; and as the driven pulley speedcontinues to increase and the driven pulley speed is above thepredetermined driven pulley speed: controlling the engine to operateunder conditions corresponding to an engine braking speed therebycausing engine braking, the engine braking speed being less than theactual engine speed.

According to some implementations of the present technology, the enginebraking speed is greater than the engagement speed.

According to some implementations of the present technology, theengagement speed is a driving pulley engagement speed.

According to some implementations of the present technology, the vehiclealso has a centrifugal clutch operatively connecting the driving pulleyto the engine. The engagement speed is a clutch engagement speed.

According to some implementations of the present technology, controllingthe engine to operate under conditions corresponding to the enginebraking speed comprises: positioning a valve controlling a supply of airto the engine at a position that is less than a position that would benecessary to operate the engine at the actual engine speed.

According to some implementations of the present technology, the valveis a throttle valve of a throttle body.

According to some implementations of the present technology, the methodfurther comprises determining an actual engine speed.

According to some implementations of the present technology, determiningthe actual engine speed includes determining a speed of rotation of adriveshaft operatively connecting the engine to the at least one groundengaging member.

According to some implementations of the present technology, determiningthe actual engine speed includes determining a vehicle speed.

According to another aspect of the present technology, there is provideda method for controlling an internal combustion engine of a vehicle. Thevehicle has the internal combustion engine and a continuously variabletransmission (CVT). The CVT has a driving pulley operatively connectedto the engine, a driven pulley, and a belt looped around the driving anddriven pulleys, the belt transmitting torque between the driving anddriven pulleys. The vehicle also has at least one ground engaging memberoperatively connected to the driven pulley. The method comprises:determining a first speed, the first speed being proportional to adriven pulley speed; determining a throttle operator position;determining a desired engine speed corresponding to the throttleoperator position; when the driven pulley speed is less than apredetermined driven pulley speed and an actual engine speed is lessthan an engine speed causing a driving pulley speed to be a drivingpulley engagement speed: controlling the engine to increase the actualengine speed to increase the driving pulley speed to be at least thedriving pulley engagement speed; and when the driven pulley speed isabove the predetermined driven pulley speed, the actual engine speed isgreater than the engine speed causing the driving pulley speed to be thedriving pulley engagement speed, and the desired engine speed is lessthan the engine speed causing the driving pulley speed to be the drivingpulley engagement speed: controlling the engine to operate underconditions corresponding to an engine braking speed thereby causingengine braking, the engine braking speed being less than the actualengine speed.

According to some implementations of the present technology, the enginebraking speed is greater than the engine speed causing the drivingpulley speed to be the driving pulley engagement speed.

According to some implementations of the present technology, the drivingpulley speed is equal to the actual engine speed.

According to some implementations of the present technology, when thedriven pulley speed is less than the predetermined driven pulley speedand the actual engine speed is less than the engine speed causing thedriving pulley speed to be the driving pulley engagement speed, themethod further comprises: controlling the engine to increase the actualengine speed as the driven pulley speed increases.

According to some implementations of the present technology, the methodfurther comprises determining the engine braking speed. Determining theengine braking speed comprises multiplying the driven pulley speed by aCVT target ratio.

According to some implementations of the present technology, determiningthe engine braking speed further comprises: subtracting an engine speedoffset from a result of the driven pulley speed being multiplied by theCVT target ratio.

According to some implementations of the present technology, the CVTtarget ratio is based on the actual engine speed.

According to some implementations of the present technology, the enginespeed offset increases as the actual engine speed increases.

According to some implementations of the present technology, the vehiclealso has a geared transmission operatively connecting the at least oneground engaging member to the driven pulley. The first speed is a speedof a rotating element operatively connecting the geared transmission tothe at least one ground engaging member. The method further comprisesdetermining a drive mode of the geared transmission. The driven pulleyspeed is determined by multiplying the first speed by a gear ratiocorresponding to the drive mode.

According to some implementations of the present technology, controllingthe engine to operate under conditions corresponding to the enginebraking speed comprises: positioning a valve controlling a supply of airto the engine at a position that is less than a position that would benecessary to operate the engine at the actual engine speed.

According to some implementations of the present technology, the valveis a throttle valve of a throttle body.

According to some implementations of the present technology, the methodfurther comprises determining an actual engine speed.

According to some implementations of the present technology, determiningthe actual engine speed includes determining a speed of rotation of adriveshaft operatively connecting the engine to the at least one groundengaging member.

According to some implementations of the present technology, determiningthe actual engine speed includes determining a vehicle speed.

According to another aspect of the present technology, there is provideda method for controlling an internal combustion engine of a vehicle. Thevehicle has the internal combustion engine, a valve for controlling asupply of air to the engine, a throttle operator adapted for actuationby a user of the vehicle, an electronic control unit (ECU), a valveactuator operatively connected to the valve for controlling a positionof the valve based on signals from the ECU, and a continuously variabletransmission (CVT). The CVT has a driving pulley operatively connectedto the engine, a driven pulley, and a belt looped around the driving anddriven pulleys, the belt transmitting torque between the driving anddriven pulleys. The vehicle has at least one ground engaging memberoperatively connected to the driven pulley. The method comprises:controlling, with the valve actuator based on signals from the ECU, theposition of the valve independently of a throttle operator position suchthat the driving pulley reaches a driving pulley engagement speed when apulley speed ratio is less than a maximum CVT ratio, the pulley speedratio corresponding to a driving pulley speed divided by a driven pulleyspeed.

According to some implementations of the present technology, the methodfurther comprises, once the driving pulley has reached the drivingpulley engagement speed: operating the engine independently of thethrottle operator position such that conditions under which the engineis operated correspond to an engine braking speed, the engine brakingspeed being less than an actual engine speed thereby causing enginebraking.

According to some implementations of the present technology, the enginebraking speed is greater than the driving pulley engagement speed.

According to some implementations of the present technology, operatingthe engine independently of the throttle operator position such thatconditions under which the engine is operated correspond to an enginebraking speed comprises: positioning the valve at a position that isless than a position that would be necessary to operate the engine atthe actual engine speed

According to some implementations of the present technology, controllingthe position of the valve independently of a throttle operator positionsuch that the driving pulley speed reaches the driving pulley engagementspeed comprises increasing the opening of the valve.

According to some implementations of the present technology, the valveis a throttle valve and the valve actuator is a throttle valve actuator.

According to another aspect of the present technology, there is provideda method for controlling an internal combustion engine of a vehicle. Thevehicle has the internal combustion engine, at least one ground engagingmember operatively connected to the driven pulley, and a centrifugalclutch having an input shaft operatively connected to the engine and anoutput shaft operatively connected to the at least one ground engagingmember. The method comprises determining a first speed, the first speedbeing proportional to an output shaft speed; determining a throttleoperator position; determining a desired engine speed corresponding tothe throttle operator position; when the output shaft speed is less thana predetermined output shaft speed and an actual engine speed is lessthan an engine speed causing an input shaft speed to be a clutchengagement speed: controlling the engine to increase the actual enginespeed to increase the input shaft speed to be at least the clutchengagement speed; and when the output shaft speed is above thepredetermined output shaft speed, the actual engine speed is greaterthan the engine speed causing the input shaft speed to be the clutchengagement speed, and the desired engine speed is less than the enginespeed causing the input shaft speed to be the clutch engagement speed:controlling the engine to operate under conditions corresponding to anengine braking speed thereby causing engine braking, the engine brakingspeed being less than the actual engine speed.

According to some implementations of the present technology, the enginebraking speed is greater than the engine speed causing the input shaftspeed to be the clutch engagement speed.

According to some implementations of the present technology, when theoutput shaft speed is less than the predetermined output shaft speed andthe actual engine speed is less than the engine speed causing the inputshaft speed to be the clutch engagement speed, the method furthercomprises: controlling the engine to increase the actual engine speed asthe output shaft speed increases.

According to some implementations of the present technology, controllingthe engine to operate under conditions corresponding to the enginebraking speed comprises: positioning a valve controlling a supply of airto the engine at a position that is less than a position that would benecessary to operate the engine at the actual engine speed.

According to some implementations of the present technology, the valveis a throttle valve of a throttle body.

For purposes of this application terms related to spatial orientationsuch as forwardly, rearward, left, and right, are as they would normallybe understood by a driver of the vehicle sitting thereon in a normaldriving position. Also, for purposes of this application, the terms“above”, “higher” and “greater than” when referring to a position of thethrottle valve compared to another position of the throttle valve mean aposition of the throttle valve where the throttle valve is more openedthan at the other position. Similarly the terms “below”, “lower” and“less than” when referring to a position of the throttle valve comparedto another position of the throttle valve mean a position of thethrottle valve where the throttle valve less opened than at the otherposition.

Exemplary implementations of the present method have at least one of theabove-mentioned aspects, but do not necessarily have all of them. Itshould be understood that example implementations of the present methodmay have other aspects not specifically recited herein.

Additional and/or alternative features, aspects, and advantages ofimplementations of the present vehicle will become apparent from thefollowing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present technology, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a perspective view taken from a front, left side of arecreational utility vehicle (RUV);

FIG. 2 is a schematic representation of the power train and someassociated components of the RUV of FIG. 1;

FIG. 3 is a graph illustrating the engine speed, the driven pulley speedand the idle speed set point over time in accordance with animplementation of a method for engine braking;

FIG. 4 is a graph illustrating the driven pulley speed and the idlespeed set point over vehicle speed in accordance with the method forengine braking;

FIG. 5 is a schematic representation of a function used to calculate theidle speed set point; and

FIG. 6 is a schematic representation of an alternative power train ofthe RUV of FIG. 1.

DETAILED DESCRIPTION

The present technology will be described with reference to aside-by-side recreational utility vehicle (RUV) 10. However, it iscontemplated that aspects of the present technology could be used inother types of vehicles having a continuously variable transmission(CVT) such as a straddle-type all-terrain vehicle (ATV), a snowmobile, amotorcycle, and a three-wheeled vehicle to name a few.

FIG. 1 illustrates the RUV 10. The RUV 10 has a front end 12, a rear end14, and two lateral sides 16 (left and right). The RUV 10 includes aframe 18 to which a vehicle body is mounted. The frame 18 has a frontportion 18A, a middle portion 18B and a rear portion 18C. A pair offront ground engaging members, which in the present application is apair of front wheels 20, is suspended from the front portion 18A of theframe 18 via front suspension assemblies 22A. A pair of rear groundengaging members, which in the present implementation is pair of rearwheels 20, is suspended from the rear portion 18C of the frame 18 viarear suspension assemblies 22B. Each of the four wheels 20 has a tire24. A cockpit area 26 is disposed in the middle portion 18B of the frame18. The cockpit area 26 comprises two seats 28 (left and right). Eachseat 28 is a bucket seat having a seat base and a backrest. It iscontemplated that the seats 28 could be other types of recumbent seats.Each seat 28 is also provided with a seat belt (not shown). The left andright seats 28 are mounted laterally beside each other to accommodate adriver and a passenger respectively of the RUV 10 (i.e. riders).

A roll cage 30 is connected to the frame 18 and is disposed above thecockpit area 26. The roll cage 30 is an arrangement of metal tubes thatcontributes to protecting the riders. The roll cage 30 has severalattachment points to the frame 18. The roll cage 30 further includes apair of lateral restraining members 32, one on each side of a rear partof the roll cage 30. The lateral restraining members 32 extend forwardfrom the rear part of the roll cage 30. The lateral restraining members32 are U-shaped tubes which help protect an upper body of the riders. Itis contemplated that the lateral restraining members 32 could have adifferent shape. It is also contemplated that the restraining members 32could be omitted.

The cockpit area 26 is open at the two lateral sides 16 of the RUV 10,forming two lateral passages 34 (left and right), through which theriders can ingress and egress the RUV 10. A lateral cover (not shown) isselectively disposed across each lateral passage 34. The lateral coversare made of flexible straps and flexible panels of meshed material. Whenthe riders are riding the RUV 10, the lateral covers are intended to bedisposed across the lateral passages 34. However, when the riders arenot riding the RUV 10 and they desire to either ingress or egress thecockpit area 26, the lateral covers can be opened to clear the lateralpassages 34.

A cargo rack 36 is mounted to the frame portion 18C of the frame 18rearward of the seats 28. It is contemplated that the cargo rack 36could be replaced by a cargo box pivotally mounted to the frame portion18C of the frame 18 rearward of the seats 28. It is contemplated thatthe cargo rack 36 could be omitted.

A steering device including a steering wheel 38 is disposed in front ofthe left seat 28. It is contemplated that, the steering wheel 38 couldbe disposed in front of the right seat 28. The steering device isoperatively connected to the two front wheels 20 to permit steering ofthe RUV 10. A display cluster 40 is disposed in front of the steeringwheel 38. A throttle operator in the form of a throttle pedal 42 (shownin FIG. 2) is disposed over the floor of the cockpit area 26 below thesteering wheel 38 and in front of the left seat 28.

An engine 44 (shown in FIG. 2) is mounted to the middle portion 18B offrame 18 and has a portion disposed between the right and the left seats28. The engine 44 is operatively connected to the four wheels 20 topower the RUV 10 as will be described in greater detail below. It iscontemplated that the engine 44 could be operatively connected only tothe rear wheels 20 or could selectively switch between driving two andfour wheels 20. A console 46 positioned between the right and left seats28 covers and separates the engine 44 from the driver and the passenger.The console 46 defines in part a central cooling tunnel allowing air toflow from the front end 12 of the vehicle 10 to the rear end 14 of thevehicle to cool the engine 44. The engine 44 is an internal combustion,four-stroke, V-twin engine. Accordingly, the engine 44 has two cylindersextending at an angle from each other. It is contemplated that othertypes of engines could be used. For example, the engine 44 could be atwo-stroke engine with in-line cylinders. The engine 44 transmits torqueto the wheels 20 via a continuously variable transmission (CVT) 48 and agear-type transmission 50 (FIG. 2). A shifter 52 (FIG. 2) located nearthe steering wheel 38 enables a driver to select one of a plurality ofdrive modes provided by the transmission 50. In the presentimplementation, the drive modes include park, neutral, reverse, low, andhigh. It is contemplated that the transmission 50 could have other drivemodes.

Fuel to be supplied to the engine 44 is stored in a fuel tank (notshown) disposed under the passenger seat 28. The fuel tank is mounted tothe middle portion 18B of the frame 18.

Turning now to FIG. 2, a power pack, a power train and some associatedcomponents of the RUV 10 will be described.

The engine 44 has intake and exhaust ports (not shown). An air intakemanifold (not shown) is connected to the intake ports of the engine 44to deliver air to the combustion chambers (not shown) of the engine 44.A throttle body 54 is fluidly connected to the intake manifold and isdisposed upstream thereof. The throttle body 54 has a throttle valve 56pivotally supported therein.

During operation of the engine 44, the throttle valve 56 is movablebetween a wide open throttle valve position and a minimum position. Inthe wide open throttle valve position, a maximum amount of air for thecurrent operating conditions is supplied to the engine 44. In theminimum position, the throttle valve 66 is slightly opened and a minimumamount of air for the current operating conditions is supplied to theengine 44. It is contemplated that the minimum position could correspondto the throttle valve being fully closed, in which case apertures areprovided in the throttle valve 56 or bypass passages are provided in thethrottle body 54 to provide some air to the engine 44.

In order to control the operation of the engine 44, an electroniccontrol unit (ECU) 58 is provided. The ECU 58 receives signals fromvarious sensors (some of which are described below), and sends signalsto various components to control the operation of these components basedon the signals received from the sensors. Although only one ECU 58 isshown, it is contemplated that the ECU 58 could be replaced by multiplecontrol units sharing the various functions of the ECU 58. Also, in theimplementation described, the various components connected to the ECU 58are electrically connected to the ECU 58 by wires. However, it iscontemplated that one or more of the various components could bewirelessly connected to the ECU 58 to permit the wireless exchange ofsignals therebetween.

The engine 44 has an output shaft which, in the present implementation,is the crankshaft 60 of the engine 44. It is contemplated that theoutput shaft could be a shaft operatively connected to the crankshaft 60of the engine 44. In such an implementation, it is contemplated that theoutput shaft could turn at a speed that is different from the speed ofthe crankshaft 60. An engine speed sensor 62 senses a speed of rotationof the crankshaft 60, which is referred to herein as the engine speed.The engine speed sensor 62 is electrically connected to the ECU 58 tosend a signal representative of the engine speed to the ECU 58.

The CVT 48 has a driving pulley 64, a driven pulley 66 and a drive belt68 looped around the pulleys 64, 66. In the present implementation, thedrive belt 68 is a rubber V-belt, but other types of belts arecontemplated. The driving pulley 64 is mounted on the crankshaft 60. Assuch, in the present implementation, the driving pulley speed is equalto the engine speed sensed by the engine speed sensor 62. Inimplementations where the output shaft is not the crankshaft 60, thedriving pulley 64 is mounted on the output shaft and the driving pulleyspeed can be determined from the engine speed sensor 62 based on thetransmission ratio between the crankshaft 60 and the output shaft. Thedriven pulley 66 is mounted on an input shaft 70 of the transmission 50.

The driving pulley 64 has a movable sheave 72, a fixed sheave 74 and aspider 76. The spider 76 has a plurality of pivotable centrifugalweights 78. As the driving pulley speed increases, the centrifugalweights 78 push on the movable sheave 74 to move the movable sheave 74toward the fixed sheave 72, thereby increasing the effective diameter ofthe driving pulley 64. A spring (not shown) biases the movable sheave 74away from the fixed sheave 72. At low driving pulley speeds, the spacebetween the fixed and movable sheaves 72, 74 causes the driving pulley64 to turn relative to the drive belt 68. As the driving pulley speedincreases, the fixed and movable sheaves 72, 74 move closer together andthe belt 68 is eventually sufficiently clamped between the fixed andmovable sheaves 72, 74 that torque can be transferred between thedriving pulley 64 and the belt 68. The driving pulley speed at whichthis clamping of the belt 68 occurs is referred to herein as the drivingpulley engagement speed. As the driving pulley speed increases, theeffective diameter of the driving pulley 64 increases. It iscontemplated that another type of centrifugally actuated driving pulleycould be used.

In an alternative implementation, a centrifugal clutch 75 (shown indotted lines in FIG. 2) is connected between the driving pulley 64 andthe crankshaft 60. In this implementation, the driving pulley 64constantly engages the belt 68. At low engine speeds, the centrifugalclutch 75 is disengaged and the driving pulley 64 can turn relative tothe crankshaft 60 by being driven by the driven pulley 66 via the belt68. The engine speed at which the clutch 75 is engaged is referred toherein as the clutch engagement speed.

The driven pulley 66 has a fixed sheave 80 and a movable sheave 82. Thedriven pulley 66 includes a torque-sensitive mechanism that adjusts theeffective diameter of the driven pulley 66.

The input shaft 70 of the transmission 50 on which the driven pulley 66is mounted engages an input gear (not shown) of the transmission 50. Thetransmission 50 contains a number of gears that can be selectivelyengaged to change the speed/torque ratio between the input and output ofthe transmission 50, and/or to change the direction of rotation of theinput versus the output of the transmission 50. By changing a positionof the shifter 52, the gears that are engaged in the transmission 50change, which results in the transmission 50 operating in a differentdrive mode. A shifter position sensor 84 senses a position of theshifter 52 and sends a signal representative of the shifter position tothe ECU 58. In the present implementation, the shifter 52 ismechanically connected to the transmission 50 via a push-pull cable (notshown) that moves a gear selector (not shown) thereby selecting thedrive mode. It is contemplated that instead of a mechanical connection,the transmission 50 could be provided with an electric motor coupled tothe gear selector and that the electric motor could be controlled by theECU 58 based on the signaled received by the ECU 58 from the shifterposition sensor 84. It is also contemplated that the shifter positionsensor 84 could sense a position of the gear selector.

The transmission 50 is operatively connected to a front driveshaft 86and a rear driveshaft 88. The front driveshaft 86 is connected to afront differential 90. The front differential 90 is connected to twofront half-shafts 92. The front half-shafts 92 are connected to thefront wheels 20. The rear driveshaft 88 is connected to a reardifferential 94. The rear differential 94 is connected to two rearhalf-shafts 96. The rear half-shafts 96 are connected to the rear wheels20. Universal joints (not shown) provide the connections between thedriveshafts 86, 88, differentials 90, 94, half-shafts 92, 96 and thewheels 20. It is contemplated that the driveshafts 86, 88, andhalf-shafts 92, 96, although each shown as being unitary shaft, could bemade of multiple shafts. It is also contemplated that one of thedriveshafts 86, 88 could be omitted in the case of a two-wheel drivevehicle. It is also contemplated that one of the driveshafts 86, 88could be selectively connected to the transmission 50 thereby permittingthe RUV 10 to operate in a two-wheel drive mode or a four-wheel drivemode.

A speed sensor 98 is electrically connected to the ECU 58. The speedsensor 98 senses a speed of rotation of the rear driveshaft 88 and sendsa signal representative of this speed to the ECU 58. By knowing thetransmission ratio (input speed (i.e. driven pulley side) over outputspeed (i.e. driveshaft side)) based on the signal from the shifterposition sensor 84, the ECU 58 can determine the driven pulley speed bymultiplying the speed sensed by the speed sensor 98 by the transmissionratio. The ECU 58 also uses the signal from the speed sensor 98 tocalculate the vehicle speed, based on the diameter of the wheels 20 andthe input to output ratio of the differential 94. It is contemplatedthat the speed sensor 98 could alternatively sense the speed of rotationof the driveshaft 86, one of the half-shafts 92, 96, a rotatingcomponent associated with one of the wheels 20 (a brake disk forexample), one of the wheels 20, a rotating element of one of thedifferentials 90, 94, a shaft of the transmission 50, the input shaft 70or the driven pulley 66.

A throttle operator position sensor 100 senses a position of thethrottle pedal 42. The throttle operator position sensor 100 iselectrically connected to the ECU 58 and sends a signal representativeof the position of the throttle pedal 42 to the ECU 58. The throttlepedal 42 is movable between a 0 percent throttle operator position,which is the position of the throttle pedal 42 when the drivercompletely releases the pedal 42, and a 100 percent throttle operatorposition, which is the position of the pedal 42 when the driver fullydepresses the pedal 42. The pedal 42 is biased toward the 0 percentthrottle operator position. In vehicles using a throttle operator otherthan a throttle pedal 42, such as a twist grip or a throttle lever forexample, the throttle operator position sensor 100 is adapted to sensethe position of the particular type of throttle operator. It iscontemplated that the throttle operator position sensor 100 could sensethe position of an element of the RUV 10 other than the throttle pedal42 that is moved by the throttle pedal 42, in which case the ECU 58could determine the throttle operator position by using the positionalrelationship between the throttle pedal 42 and the element.

A throttle valve actuator 102 is disposed on a left side of the throttlebody 54. The throttle valve actuator 102 is connected to the throttlevalve 56 to pivot the throttle valve 56 between its various positions.The throttle valve actuator 102 is electrically connected to the ECU 58and receives signals from the ECU 58. The throttle valve actuator 102moves the throttle valve 56 based on the signals received from the ECU58. In the present implementation, the throttle valve actuator 102 is arotary electrical motor, but other types of throttle valve actuators arecontemplated. Systems of this type are sometimes referred to asthrottle-by-wire systems.

A throttle valve position sensor 104 senses a position of the throttlevalve 56 by sensing a position of a shaft of the throttle valve actuator102. It is contemplated that the throttle valve position sensor 104could sense the position of the throttle valve 56 directly. It is alsocontemplated that the throttle valve position sensor 104 could beintegrated into the throttle valve actuator 102. The throttle valveposition sensor 104 is electrically connected to the ECU 58 and sends asignal representative of the position of the throttle valve 56 to theECU 58.

It is contemplated that in alternative implementations of the power packand of the power train, other sensors could be used in addition to orinstead of the sensors described above.

During acceleration of the RUV 10, the driver presses on the throttlepedal 42 and the engine 44 drives the crankshaft 60, which drives thedriving pulley 64. Assuming that the driving pulley 64 is turning at aspeed above the driving pulley engagement speed, the driving pulley 64engages the belt 68 and drives the belt 68, which in turn drives thedriven pulley 66. The driven pulley 66 drives the input shaft 70. Theinput shaft 70 drives the transmission 50. The transmission 50, whichoperates according to the drive mode selected by the shifter 52, drivesthe driveshafts 86, 88 (unless the transmission 50 is in the neutralmode). The driveshafts 86, 88 drive their respective differentials 90,94. The differentials 90, 94 then drive their respective wheels 20 viatheir respective half-shafts 92, 96.

With the RUV 10 in movement and the driving pulley 64 operating abovethe driving pulley engagement speed, when the driver releases thethrottle pedal 42, the ECU 58 sends a signal to the throttle valveactuator 102 to close the throttle valve 56. As such, the engine 44 isnow being controlled under conditions corresponding to an engine speedthat is less than the actual engine speed. Under these conditions, thewheels 20 drive the half-shafts 92, 96, which drive the differentials80, 94, which drive the driveshafts 86, 88, which drive the transmission50. The transmission 50, which operates according to the drive modeselected by the shifter 52, drives the input shaft 70 (unless thetransmission 50 is in the neutral mode). The input shaft 70 drives thedriven pulley 66, which drives the belt 68. Since the driving pulley 64is operating above the driving pulley engagement speed, the drivingpulley 64 clamps the belt 68 and the belt 68 drives the driving pulley64. The driving pulley 64 drives the crankshaft 60. The speed at whichthe driving pulley 64 drives the crankshaft 60 (i.e. the actual enginespeed) is greater than the speed at which the engine 44 is beingcontrolled to run. Since the engine 44 is being controlled to run underconditions corresponding to an engine speed that is less than the actualengine speed (i.e. the throttle valve 56 is not sufficiently opened),engine braking is applied. For example, if the driving pulley 64 drivesthe engine 44 at an actual engine speed of 2200 RPM, but the position ofthe throttle valve 56 corresponds to a position at which the engine 44would normally be running at 1900 RPM, the conditions under which theengine 44 is being controlled to run result in insufficient air beingsupplied to the engine 44 compared to what would normally be necessaryto drive the engine 44 at 2200 RPM. As a result, a vacuum is created inthe engine 44 which resists the torque being applied by the drivingpulley 64 to the crankshaft 60, and engine braking occurs. The greaterthe difference is between the actual engine speed and the speedcorresponding to the conditions under which the engine 44 is beingcontrolled to operate, the greater the amount of engine braking is.

In accordance with the present technology, with the RUV 10 in movement,or starting to move from rest, such as when starting to go down a hill,and the driving pulley 64 operating below the driving pulley engagementspeed, when the driver releases the throttle pedal 42 (if it is notalready released), the ECU 58 sends a signal to the throttle valveactuator 102 to close the throttle valve 56 to a position correspondingto an idle speed set point as will be described further below. As in theconditions described above, under these conditions, the wheels 20 drivethe half-shafts 92, 96, which drive the differentials 80, 94, whichdrive the driveshafts 86, 88, which drive the transmission 50. Thetransmission 50, which operates according to the drive mode selected bythe shifter 52, drives the input shaft 70 (unless the transmission 50 isin the neutral mode). The input shaft 70 drives the driven pulley 66,which drives the belt 68. Contrary to the conditions described above,since the driving pulley 64 is operating below the driving pulleyengagement speed, the driving pulley 64 does not clamp the belt 68 andthe belt 68 does not drive the driving pulley 64. As such, no enginebraking is initially provided. The present technology provides a method,described below, through which engine braking will be provided as thedriven pulley speed and vehicle speed increase without the need of amechanical device, such as a one-way clutch, as in the prior art.

The present method will be described with reference to FIGS. 3 to 5. Thegraphs of FIGS. 3 and 4 illustrate scenarios applying the present methodwhere the RUV 10 is going down a hill, with the throttle pedal 42completely released, and the RUV 10 accelerating due to gravity. In thegraph of FIG. 3, the actual engine speed is illustrated by a dashedline. In the graphs of FIGS. 3 and 4, the driven pulley speed isillustrated by a dashed-dot line, and the values of the driven pulleyspeed have been multiplied by the maximum CVT ratio, which in thepresent exemplary implementation is 2.85. The CVT ratio is the ratio ofthe driving pulley speed over the driven pulley speed and it is also theratio of the effective driven pulley diameter over the effective drivingpulley diameter. The maximum CVT ratio is the CVT ratio when the drivenpulley 66 is at its maximum effective diameter and the driving pulley 64is at its minimum effective diameter. By multiplying the driven pulleyspeed by the maximum CVT ratio, the dashed-dot line also illustrates thespeed at which the driving pulley 64 would be operating with the drivingpulley 64 engaging the belt 68 and the CVT 48 being at the maximum CVTratio. In the graphs of FIGS. 3 and 4, the idle speed set point isillustrated by a solid line. The idle speed set point is a valuecalculated by the ECU 58 of the conditions, including the position ofthe throttle valve 56, under which the engine 44 should be operated toapply the present method. In the present implementation, the idle speedset point is the minimum desired engine speed for a given driven pulleyspeed. In the present method, the ECU 58 controls the engine 44 tooperate under conditions that would provide the idle speed set point ifno external forces accelerating the RUV 10 were acting on the RUV 10. Inthe present scenarios, the external force is the force component ofgravity resulting from the RUV 10 going down a hill. An implementationof a method of calculating the idle set point will be discussed ingreater detail below with respect to FIG. 5. It should be understoodthat the graphs of FIGS. 3 and 4 correspond to a specific example underspecific conditions and it should be understood that the shape of thevarious curves and the various values, such as the driving pulleyengagement speed, would differ for a different CVT, vehicle, engineand/or hill incline to name a few of the variables that would affect theappearance of the curves.

During operation of the RUV 10, the ECU 58 determines the desired enginespeed based on the signals receive from at least the throttle operatorposition sensor 100. The ECU 58 may also additionally use signals fromone or more of the other sensors to determine the desired engine speed.If the desired engine speed is less than the idle speed set point forthe current driven pulley speed, then the ECU 58 controls the positionof the throttle valve 56, via the throttle valve actuator 102, and otherengine parameters to operate under conditions corresponding to the idlespeed set point. This occurs without any driver intervention. Should thedesired engine speed be greater than the idle speed set point, then theECU 58 controls the position of the throttle valve 56 and other engineparameters to operate under conditions corresponding to the desiredengine speed. For example, when the driver completely releases thethrottle pedal 42, this is indicative of a desired engine speedcorresponding to the minimum operating speed of the engine 44, which forthe example provided in FIG. 3 corresponds to about 1250 RPM. However,should the idle speed set point for the given driven pulley speed behigher than this, the ECU 58 will operate the engine under conditionscorresponding to the idle speed set point.

In an alternative implementation (not shown), an air bypass valve isprovided in an idle air bypass passage and the position of the airbypass valve is controlled by an air bypass valve actuator. As thedetails of the construction of a throttle body having such an idle airbypass passage, valve and actuator are believed to be known to a personskilled in the art, they will not be provided herein. In such animplementation, if the desired engine speed is less than the idle speedset point for the current driven pulley speed, then the ECU 58 controlsthe position of the air bypass valve, via the air bypass valve actuator,and other engine parameters to operate under conditions corresponding tothe idle speed set point. This occurs without any driver intervention.

Turning now to FIG. 3, the method will be explained according to thescenario described above (i.e. the RUV 10 is going down a hill, with thethrottle pedal 42 completely released, and the RUV 10 accelerating dueto gravity) in terms of speed versus time. In the present scenario, theshifter 52 is in the high position and the transmission 50 operates inhigh mode accordingly. Also in the present scenario, the driving pulley64 does not initially engage the belt 68. As the RUV 10 accelerates dueto gravity, the driven pulley speed increases linearly. In the presentimplementation, when the driven pulley speed is less than about 439 RPM(1250 RPM divided by 2.85 (maximum CVT ratio), range A in FIG. 3), theidle speed set point is constant at 1250 RPM, which corresponds to theminimum operating speed of the engine 44. The ECU 58 controls the engine44 to operate under conditions corresponding to the constant idle setpoint. Under these conditions, the throttle valve actuator 102 moves thethrottle valve 56 to its minimum position (i.e. at its position wherethe least amount of air is supplied to the engine). As the drivingpulley 64 is operating below the driving pulley engagement speed, noexternal torques from the drive belt 68 are being applied on thecrankshaft 60, and the actual engine speed corresponds to the idle speedset point (i.e. 1250 RPM).

Once the driven pulley speed exceeds the minimum operating speed of theengine 44 (i.e. 439 RPM) as the RUV 10 continues to accelerate, which inthe graph occurs at about 2.2 seconds, the idle speed set pointincreases as the driven pulley speed increases (range B in FIG. 3). Ascan be seen, the idle speed set point increases at a slower rate thanthe driven pulley speed, but it is contemplated that the idle speed setpoint could increase at the same or at greater rate than the drivenpulley speed. As the ECU 58 continues to operate the engine 44 underconditions corresponding to the idle speed set point, the throttle valve56 is increasingly opened as the idle speed set point increases. As aresult, since the conditions under which the ECU 58 operates the engine44 correspond to an engine speed (i.e. the idle speed set point) that isgreater than the actual engine speed (i.e. the throttle valve 56 issufficiently opened), the engine 44 accelerates and the actual enginespeed sensed by the engine speed sensor 62 increases.

As the RUV 10 continues to accelerate, the driven pulley speed alsocontinues to increase, and the idle speed set point eventually increasesto the driving pulley engagement speed (lower end of range C in FIG. 3).In the present implementation, this occurs at about 3.1 seconds when theidle speed set point reaches the driving pulley engagement speed of 1700RPM. The idle speed set point continues to increase and shortly afterthe idle speed set point has reached the driving pulley engagement speed(i.e. with the idle speed set point at the upper end of range C), atabout 3.2 seconds, due to the delay in engine response, the actualengine speed also reaches the driving pulley engagement speed (point Ein FIG. 3). Once the actual engine speed reaches the driving pulleyengagement speed, the driving pulley 64 also turns at the driving pulleyengagement speed and clamps the belt 68. It is contemplated that therate at which the idle speed set point increases prior to the drivingpulley 64 reaching the driving pulley engagement speed could be modifiedfrom what is illustrated in FIG. 3 such that the driving pulley 64reaches the driving pulley speed sooner or later than illustrated.

As can be seen, once the driving pulley 64 engages the belt 68, thedriving pulley speed quickly increases. This is because torque is nowtransmitted to the driving pulley 64 by the belt 68 and the drivingpulley speed that would correspond to the driven pulley speed (i.e.driven pulley speed multiplied by the CVT ratio) is higher than thedriving pulley speed due to the acceleration the RUV 10 has undergone.As described above, when the driven pulley speed multiplied by the CVTratio is higher than the driving pulley speed with the driving pulley 64engaging the belt 68, the wheels 20 drive the half-shafts 92, 96, whichdrive the differentials 80, 94, which drive the driveshafts 86, 88,which drive the transmission 50, which drives the input shaft 70 (unlessthe transmission 50 is in the neutral mode), which drives the drivenpulley 66, which drives the belt 68, which drives the driving pulley 64,which finally drives the crankshaft 60.

Once the driving pulley speed exceeds the idle speed set point (range Din FIG. 3), which determines the conditions under which the engine 44 isbeing controlled under the above described operating conditions, thespeed at which the driving pulley 64 drives the crankshaft 60 (i.e. theactual engine speed) is greater than the speed at which the engine 44 isbeing controlled to run (i.e. the idle speed set point). Since the idlespeed set point is less than the actual engine speed, engine braking isapplied because the throttle valve 56 is being controlled to be at aposition that is less than a position that would be necessary to operatethe engine 44 at the actual engine speed. The effects of engine brakingcan be seen in FIG. 3 by the slope of the driven pulley speed thatstarts decreasing in range D, thus indicating a reduction in theacceleration of the vehicle 10.

As can be seen in FIG. 3, once the driving pulley speed exceeds the idlespeed set point, the idle speed set point is first decreased slightly,then increased, then decreased almost to the driving pulley engagementspeed, and then constantly increased at a small rate. This controlstrategy provides a smooth transition to the engine braking condition,but it is contemplated that it could differ from what is illustrated. Inthe present implementation, the idle speed set point is alwaysmaintained above the driving pulley engagement speed once the drivingpulley 64 has reached the driving pulley engagement speed. However, itis contemplated that the idle speed set point could be reduced below thedriving pulley engagement speed once the driving pulley 64 has reachedthe driving pulley engagement speed. As explained above, the amount ofengine braking being applied increases as the difference between thedriving pulley speed and the speed at which the engine 44 is beingcontrolled to operate (i.e. the idle speed set point) increases. Assuch, once the driving pulley 64 engages the belt 68, the value of theidle speed set point is determined based on the amount of engine brakingthat is desired. In the present implementation, once the driving pulley64 has reached the driving pulley engagement speed, the idle speed setpoint is controlled to reduce the acceleration of the RUV 10. Since byoperating the engine 44 under conditions corresponding to the idle speedset point results in engine braking once the driving pulley 64 hasreached the driving pulley engagement speed, this portion of the idlespeed set point is said to be an engine braking speed. As can also beseen in range D of FIG. 3, once the driving pulley speed exceeds theidle speed set point, the driving pulley speed increases until itcatches up to the speed at which it should be operating for the currentdriven pulley speed (i.e. the driven pulley speed multiplied by the CVTratio).

Accordingly, in the present method, when the driven pulley speedincreases and the driving pulley speed is below the driving pulleyengagement speed, the ECU 58 controls the engine 44 to operate underconditions corresponding to the idle speed set point which increases asthe driven pulley speed increases. This is done, for example, byincreasing the amount of air introduced into the engine 44 by opening ofthe throttle valve 56 or by opening an air bypass valve should one bepresent independently of the position of the throttle pedal positionsuch that the air introduced into the engine 44 is greater than thatwhich would be introduced to the engine 44 were the valve position bethe one corresponding to the position of the throttle pedal 42. As aresult, the actual engine speed, and therefore the driving pulley speed,increases. Should the driven pulley speed continue to increase, thedriving pulley speed eventually reaches the driving pulley engagementspeed, thus permitting engine braking. Once the driving pulley 64engages the belt 68, controlling the engine 44 to operate underconditions corresponding to the idle speed set point results in enginebraking. This control of the engine 44 by the ECU 58 is doneindependently of driver input (i.e. the driver does not have to pressthe throttle pedal 42 in order to increase the driving pulley speed toinitiate engine braking).

The above method can also be applied in terms of the ratio of pulleyspeeds. When the driving pulley 64 is operating at a speed below thedriving pulley engagement speed and the actual driving pulley speeddivided by the actual driven pulley speed (i.e. the ratio of pulleyspeeds) is less than the maximum CVT ratio (i.e. the maximum ratiopossible with the belt 68 engaged by the driving pulley 64), which is2.85 in the present exemplary implementation, the ECU 58 controls theoperation of the engine 44 such that the driving pulley 64 reaches thedriving pulley engagement speed. As discussed above, the ECU 58determines the driving and driven pulley speeds from the sensors 62 and98 respectively. Accordingly, when the CVT ratio is less than 2.85, theECU 58 controls the engine 44 to increase the idle speed set point toforce the engagement of the driving pulley 64. This is done, forexample, by increasing the amount of air introduced into the engine 44by opening the throttle valve 56 or by opening an air bypass valveshould one be present. Once the driving pulley 64 engages the belt 68,controlling the engine 44 to operate under conditions corresponding tothe idle speed set point results in engine braking. As above, thiscontrol of the engine 44 by the ECU 58 is done independently of driverinput (i.e. the driver does not have to press the throttle pedal 42 inorder to increase the driving pulley speed). As such, the amount of airintroduced to the engine 44 is greater than that which would beintroduced to the engine 44 were the throttle valve position be the onecorresponding to the position of the throttle pedal 42.

Turning now to FIG. 4, the method will be explained according to thescenario described above (i.e. the RUV 10 is going down a hill, with thethrottle pedal 42 completely released, and the RUV 10 accelerating dueto gravity) in terms of rotation speed versus vehicle speed. In thepresent scenario, the shifter 52 is in the high position and thetransmission 50 operates in high mode accordingly. Also in the presentscenario, the driving pulley 64 does not initially engage the belt 68.In the present implementation, the vehicle speed is calculated using thesignal received from the speed sensor 98. It is contemplated that thevehicle speed could be obtained from other sensors or inputs. Forexample, the vehicle speed could be obtained from a global positionssystem that obtains the vehicle speed by determining the displacement ofthe RUV 10 over time. It should be noted that the engine speed line(i.e. dotted line) in FIG. 4 is not visible prior to point E and shortlyafter point E and can only be seen between point E and the dashed-dotline. This is because before point E, the engine speed line overlaps thesolid line and that shortly after point E the engine speed line overlapsthe dashed-dot line. As there is a direct correlation between vehiclespeed and driven pulley speed, the ECU 58 controls the engine 44 tooperate under conditions corresponding to the idle speed set point in amanner similar to the one described above for FIG. 3. For simplicity, inview of this and in view of the direct correlation between engine speedand driven pulley speed, the control of the engine 44 over these rangeswill not be explained herein in detail. Prior to the driving pulley 64reaching the driving pulley engagement speed (i.e. point E), the ECU 58controls the operation of the engine 44 so as to increase the enginespeed as the vehicle speed increases, and therefore the driven pulleyspeed, until the driving pulley engagement speed is reached. Once thedriving pulley speed reaches the driving pulley engagement speed (i.e.point E), the actual engine speed increases such that the driving pulleyspeed matches the driving pulley speed at which it should be operatingfor the current driven pulley speed (i.e. the driven pulley speedmultiplied by the CVT ratio), and the ECU 58 controls the engine 44 tooperate under conditions corresponding to an idle speed set point thatis less than the actual engine speed to cause engine braking, similarlyto what is described above with respect to FIG. 3. In the presentimplementation, once the engine braking speed reaches 2200 RPM, theengine braking speed is held constant at this value by the ECU 58. It iscontemplated that the engine braking speed could alternatively keepincreasing as vehicle speed increases or that it could instead decrease.

In the implementation described above with respect to FIG. 2 in whichthe RUV 10 is provided with the centrifugal clutch 75, the ECU 58 wouldcontrol the operation of the engine 44 in the same manner as describedabove with respect to FIGS. 3 and 4, but instead of the control beingbased relative to the driving pulley engagement speed, it is relative tothe clutch engagement speed. For example, should the clutch 75 bedisengaged, with the throttle pedal 42 being completely released and thedriven pulley speed increasing, the ECU 58 controls the operation of theengine 44 to increase the engine speed as the driven pulley speedincreases until the clutch engagement speed is reached and once theclutch 75 is engaged, the ECU 58 controls the operation of the engine 44to cause engine braking.

Turning now to FIG. 5, an exemplary method used by the ECU 58 todetermine the idle speed set point will be described. In the presentimplementation, the ECU 58 is constantly determining the idle speed setpoint for the current operating conditions of the RUV 10. It is howevercontemplated that the ECU 58 could only determine the idle speed setpoint when certain conditions exist. For example, it is contemplatedthat the ECU 58 could only determine the idle speed set point when thethrottle pedal 42 is actuated by less than a certain amount or iscompletely released by the driver of the RUV 10.

At step 200, the ECU 58 determines the current driven pulley speed. TheECU 58 receives signals from the sensor 98 that senses a speed ofrotation of the rear driveshaft 88. From these signals, the ECU 58determines the speed of the rear driveshaft 88. The ECU 58 also receivesa signal from the shifter position sensor 84 that senses the position ofthe shifter 52. From this signal, the ECU 58 determines the operationmode of the transmission 50 and therefore the corresponding gear ratioof the transmission 50. The ECU 58 obtains the driven pulley speed fromthe rear driveshaft 88 speed and the gear ratio of the transmission 50.As previously mentioned, it is also contemplated that the ECU 58 coulddetermine the driven pulley speed directly from a sensor sensing thespeed of rotation of the driven pulley 66 or the transmission inputshaft 70, in which case it would not be necessary to determine theoperation mode of the transmission 50 to determine the driven pulleyspeed.

At step 202, the ECU 58 determines the actual engine speed from signalsreceived from the engine speed sensor 62. Using the actual engine speeddetermined at step 202, at step 204 the ECU 58 determines a CVT targetratio corresponding to the actual engine speed. The CVT target ratio isdetermined by finding, in a lookup table or graph stored in the ECU 58or a separate memory, the CVT target ratio corresponding to the actualengine speed. For engine speeds that are between engine speeds in thelookup table, the corresponding CVT target ratio is determined throughinterpolation. The value of the CVT target ratio decreases as the actualengine speed increases. At step 206, the ECU 58 multiplies the drivenpulley speed determined at step 200 by the CVT target ratio determinedat step 204. It is contemplated that steps 204 and 206 could be omitted.

Using the actual engine speed determined at step 202, at step 208 theECU 58 determines an engine speed offset. The engine speed offset isdetermined by finding, in a lookup table or graph stored in the ECU 58or a separate memory, the engine speed offset corresponding to theactual engine speed. For engine speeds that are between engine speeds inthe lookup table, the corresponding engine speed offset is determinedthrough interpolation. The value of the engine speed offset increases asthe actual engine speed increases. At step 210, the ECU 58 subtracts theengine speed offset determined at step 208 from the result of themultiplication of step 206. The result of this subtraction (step 212) isthe idle speed set point for the driven pulley speed determined at step200 and the actual engine speed determined at step 202 used in themethod described above with respect to FIG. 3. It is contemplated thatsteps 208 and 210 could be omitted.

The values shown for the CVT target ratio and engine speed offset shownin FIG. 5 are only one example. These values can be determinedexperimentally according to the desired handling behavior of the RUV 10and will vary depending on the specific construction of the RUV 10, theengine 44 and the CVT 48.

FIG. 6 illustrates an alternative implementation of the power train ofthe RUV 10. For simplicity, components of the power train illustrated inFIG. 6 that correspond to those previously described with respect toFIG. 2 have been labelled with the same reference numeral and will notbe described again.

In the implementation of FIG. 6, the RUV 10 has an engine 44′. Theengine 44′ has a rearward extending output shaft 60′. The output shaft60′ is operatively connected to the crankshaft of the engine 44′ bybevel gears for example. The RUV 10 also has a transmission 50′ that isspaced from the engine 44′. The transmission 50′ has a forwardlyextending input shaft 70′. A centrifugal clutch 75′ is connected betweenthe output shaft 60′ of the engine 44′ and the input shaft 70′ of thetransmission 50′. As such in the present implementation, the outputshaft 60′ of the engine 44′ is the input shaft of the centrifugal clutch75′ and the input shaft of the transmission 50′ is the output shaft ofthe centrifugal clutch 75′. At low output shaft speeds, the centrifugalclutch 75′ is disengaged and the input shaft 70′ of the transmission 50′can turn relative to the output shaft 60′ of the engine 44′. The outputshaft speed at which the clutch 75′ is engaged is referred to herein asthe clutch engagement speed. It is contemplated that the clutch 75′could not be connected directly to the output shaft 60′ of the engine44′, in which case the clutch engagement speed would be the speed of theinput shaft of the clutch 75′ at which the clutch 75′ is engaged andthat there is a corresponding engine speed that causes the input shaftof the clutch 75′ to turn at the clutch engagement speed. For example,the clutch 75′ could be connected between a driven pulley of a CVT andthe input shaft of a transmission. In another example, the clutch 75′could be connected between the transmission and the driveshafts 86, 88.

In a RUV 10 having this type of power train, the ECU 58 controls theoperation of the engine 44′ in the same manner as described above withrespect to FIGS. 3 and 4, but instead of the control being basedrelative to the driving pulley engagement speed, driven pulley speed anddriving pulley speed, it is relative to the clutch engagement speed, theoutput shaft speed of the clutch 75′ (i.e. the speed of the input shaft70′ of the transmission 50′) and the input shaft speed of the clutch 75′(i.e. the speed of the output shaft 60′ of the engine 44′) respectively.For example, should the clutch 75′ be disengaged, with the throttlepedal 42 being completely released and the output shaft speed (i.e. thespeed of the input shaft 70′ of the transmission 50′) increasing, theECU 58 controls the operation of the engine 44 to increase the enginespeed as the output shaft speed increases until the clutch engagementspeed is reached and once the clutch 75′ is engaged, the ECU 58 controlsthe operation of the engine 44 to cause engine braking. The control ofthe engine speed to cause engine braking is independent of the operatorand the throttle pedal position.

Modifications and improvements to the above-described implementations ofthe present technology may become apparent to those skilled in the art.The foregoing description is intended to be exemplary rather thanlimiting. The scope of the present technology is therefore intended tobe limited solely by the scope of the appended claims.

What is claimed is:
 1. A method for controlling an internal combustionengine of a vehicle, the vehicle comprising: the internal combustionengine; a continuously variable transmission (CVT) comprising: a drivingpulley operatively connected to the engine; a driven pulley; and a beltlooped around the driving and driven pulleys, the belt transmittingtorque between the driving and driven pulleys; and at least one groundengaging member operatively connected to the driven pulley; the methodcomprising: determining a first speed, the first speed beingproportional to a driven pulley speed; determining a throttle operatorposition; determining a desired engine speed corresponding to thethrottle operator position; when the driven pulley speed is less than apredetermined driven pulley speed and an actual engine speed is lessthan an engine speed causing a driving pulley speed to be a drivingpulley engagement speed: controlling the engine to increase the actualengine speed to increase the driving pulley speed to be at least thedriving pulley engagement speed; and when the driven pulley speed isabove the predetermined driven pulley speed, the actual engine speed isgreater than the engine speed causing the driving pulley speed to be thedriving pulley engagement speed, and the desired engine speed is lessthan the engine speed causing the driving pulley speed to be the drivingpulley engagement speed: controlling the engine to operate underconditions corresponding to an engine braking speed thereby causingengine braking, the engine braking speed being less than the actualengine speed.
 2. The method of claim 1, wherein the engine braking speedis greater than the engine speed causing the driving pulley speed to bethe driving pulley engagement speed.
 3. The method of claim 1, whereinthe driving pulley speed is equal to the actual engine speed.
 4. Themethod of claim 1, wherein when the driven pulley speed is less than thepredetermined driven pulley speed and the actual engine speed is lessthan the engine speed causing the driving pulley speed to be the drivingpulley engagement speed, the method further comprises: controlling theengine to increase the actual engine speed as the driven pulley speedincreases.
 5. The method of claim 1, further comprising determining theengine braking speed; wherein determining the engine braking speedcomprises: multiplying the driven pulley speed by a CVT target ratio. 6.The method of claim 5, wherein determining the engine braking speedfurther comprises: subtracting an engine speed offset from a result ofthe driven pulley speed being multiplied by the CVT target ratio.
 7. Themethod of claim 6, wherein the CVT target ratio is based on the actualengine speed.
 8. The method of claim 6, wherein the engine speed offsetincreases as the actual engine speed increases.
 9. The method of claim1, wherein the vehicle further comprises a geared transmissionoperatively connecting the at least one ground engaging member to thedriven pulley; wherein the first speed is a speed of a rotating elementoperatively connecting the geared transmission to the at least oneground engaging member; wherein the method further comprises determininga drive mode of the geared transmission; and wherein the driven pulleyspeed is determined by multiplying the first speed by a gear ratiocorresponding to the drive mode.
 10. The method of claim 1, whereincontrolling the engine to operate under conditions corresponding to theengine braking speed comprises: positioning a valve controlling a supplyof air to the engine at a position that is less than a position thatwould be necessary to operate the engine at the actual engine speed. 11.The method of claim 10, wherein the valve is a throttle valve of athrottle body.
 12. The method of claim 1, further comprising determiningan actual engine speed.
 13. The method of claim 12, wherein determiningthe actual engine speed includes determining a speed of rotation of adriveshaft operatively connecting the engine to the at least one groundengaging member.
 14. The method of claim 12, wherein determining theactual engine speed includes determining a vehicle speed.
 15. A methodfor controlling an internal combustion engine of a vehicle, the vehiclecomprising: the internal combustion engine; at least one ground engagingmember operatively connected to the driven pulley; and a centrifugalclutch having an input shaft operatively connected to the engine and anoutput shaft operatively connected to the at least one ground engagingmember; the method comprising: determining a first speed, the firstspeed being proportional to an output shaft speed; determining athrottle operator position; determining a desired engine speedcorresponding to the throttle operator position; when the output shaftspeed is less than a predetermined output shaft speed and an actualengine speed is less than an engine speed causing an input shaft speedto be a clutch engagement speed: controlling the engine to increase theactual engine speed to increase the input shaft speed to be at least theclutch engagement speed; and when the output shaft speed is above thepredetermined output shaft speed, the actual engine speed is greaterthan the engine speed causing the input shaft speed to be the clutchengagement speed, and the desired engine speed is less than the enginespeed causing the input shaft speed to be the clutch engagement speed:controlling the engine to operate under conditions corresponding to anengine braking speed thereby causing engine braking, the engine brakingspeed being less than the actual engine speed.
 16. The method of claim15, wherein the engine braking speed is greater than the engine speedcausing the input shaft speed to be the clutch engagement speed.
 17. Themethod of claim 15, wherein when the output shaft speed is less than thepredetermined output shaft speed and the actual engine speed is lessthan the engine speed causing the input shaft speed to be the clutchengagement speed, the method further comprises: controlling the engineto increase the actual engine speed as the output shaft speed increases.18. The method of claim 15, wherein controlling the engine to operateunder conditions corresponding to the engine braking speed comprises:positioning a valve controlling a supply of air to the engine at aposition that is less than a position that would be necessary to operatethe engine at the actual engine speed.
 19. The method of claim 18,wherein the valve is a throttle valve of a throttle body.